There exists in the art a variety of golf clubs wherein the head is adjustable relative to the shaft. For example, U.S. Pat. Nos. 4,878,666 to Hosoda; 2,520,702 to Verderber; 1,258,212 to Goodrich; 1,206,104 to Goodrich; and 1,083,434 to Curry disclose golf clubs wherein the head is variable in its angle relative to the shaft. In particular, the club heads disclosed in the aforementioned patents rotate or pivot about a longitudinal axis extending through the club head from heel to toe. Such adjustment allows variance of the loft angle or "angle of approach" between the head and the golf ball which it strikes. This type of adjustment is particularly desirable for woods, irons, and other clubs used for golf shots in which the ball is lifted from the playing surface by the club. In the case of the aforementioned patents, the adjustable head also permits each club to be used as a putter as well as an iron of variable loft angle. In other words, the primary feature of these clubs is versatility for use off the green as well as on it. Thus, the adjustment for putting merely involves locating the striking face of the club in a substantially vertical plane.
In putting, however, there are considerations other than merely locating the plane of the putter striking face. For example, it would be desirable if the longitudinal axis of the putter head were positioned relative to the axis of the putter shaft at the optimum angle for the particular lie of the ball on the green, i.e., the "lie angle." Such adjustment is useful in putting balls lying on a variety of terrains and inclines. Heretofore, a player desiring to change the lie angle of the club head has sometimes resorted to measures as drastic as bending the club shaft. Another disadvantage of the above prior art adjustable clubs is that they are not convertible for use by both right- and left-handed players. It would be desirable, therefore, to provide a single golf putter which not only can be used by both right- and left-handed players, but also can accommodate various lie angles of the ball on the putting surface.
With golf clubs, and in particular putters, it would also be desirable to adjust the center of percussion of the club head, popularly referred to by golfers as the "sweet spot." The sweet spot is that point on the face of the head where contact with the ball results in the least amount of torque about the shaft. The location of the center of percussion or sweet spot is a function of the shape, size, and mass of the head, as well as the relative distance of the hosel from the toe and heel of the head. Thus, for example, moving the hosel closer to the toe moves the sweet spot in that same direction. Accordingly, it would be advantageous to have a putter wherein the sweet spot is adjustable along the longitudinal axis of the head between the heel and toe thereof.
It would also be desirable to provide a golf putter with a replaceable head. Some golfers carry several putters having differently designed club heads, e.g., different club head weights. With a replaceable head putter, only the different putter heads need be carried rather than several different complete putters.